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Iron has been emerging as a key contributor to aging-associated, chronic disorders due to the propensity for generating reactive oxygen species. To date, there are a limited number of publications exploring the role of iron in the pathogenesis of primary/age-related osteoarthritis (OA). The objective of this study was to determine whether reduced iron via pharmacologic iron chelation with deferoxamine (DFO) affected the development and/or severity of cartilage lesions in a primary OA model. At 12-weeks-of-age, 15 male Dunkin-Hartley guinea pigs received either 46 mg/kg DFO (n = 8) or vehicle control (n = 7) injected subcutaneously twice daily for five days each week. Movement changes, captured via overhead enclosure monitoring, were also determined. Termination occurred at 30-weeks-of-age. Iron was quantified in serum, urine, liver, and femoral head articular cartilage. Left knees were evaluated for: structural changes using histopathology guidelines; and immunohistochemistry. Gene expression analysis was conducted on right knee articular cartilage. DFO reduced iron levels in femoral head articular cartilage (p = 0.0006) and liver (p = 0.02), and increased iron within urine (p = 0.04) and serum (p = 0.0009). Mobility of control animals declined, while the DFO group maintained activity levels similar to the first month of treatment (p = 0.05). OA-associated cartilage lesions were reduced in knees of DFO animals (p = 0.0001), with chondrocyte hypocellularity a key histologic difference between groups (p 0.0001). DFO-receiving animals had increased immunostaining for phosphorylated adenosine monophosphate activated protein kinase alpha within knee articular cartilage; lower transcript counts of several proapoptotic genes (p = 0.04-0.0004) and matrix-degrading enzymes (p = 0.02-0.0001), and increased expression of the anti-apoptotic gene Bcl-2 (p 0.0001) and a tissue inhibitor of matrix-metalloproteinases (p = 0.03) were also observed. These results suggest that iron chelation delayed the progression of primary OA in an animal model and could hold potential as a translational intervention. These findings provide expanded insight into factors that may contribute to the pathogenesis of primary OA.

Summary Objective Iron is emerging as a key player in aging-associated diseases due to its propensity for driving free radical formation. Studies examining the role of iron in the pathogenesis of primary osteoarthritis (OA) are limited. Our objective was to establish a direct relationship between excess iron and OA by administering iron dextran to a guinea pig strain with decreased propensity for developing this disease. Design Twenty, 12-week-old Strain 13 guinea pigs received either iron dextran or dextran control intraperitoneally once weekly for 4 weeks; termination occurred at 16 weeks of age. Iron levels were determined systemically (serum and liver) and within diarthrodial joints [femoral head articular cartilage and infrapatellar fat pads (IFPs) of knee joints]. One knee was collected to score structural changes associated with OA via microcomputed tomography (microCT) and histology using published grading schemes. Articular cartilage and IFPs were harvested from contralateral knees for gene expression analyses. Results Iron overload was confirmed systemically via increased serum iron and liver iron concentration. Articular cartilage and IFPs in the iron dextran group also had higher levels of iron. Excess iron worsened knee OA using both microCT and histologic scoring systems. Gene analyses revealed that exogenous iron altered the expression of iron trafficking proteins, select cytokines, and structural components of cartilage. Conclusion These results demonstrate that systemic iron overload caused cellular iron accumulation in the knee joint. This excess iron is associated with increased expression of local inflammatory mediators and early onset and progression of knee joint OA in Strain 13 animals.

The progression of rheumatoid arthritis involves the thickening of the synovial lining due to the proliferation of fibroblast-like synoviocytes (FLS) and infiltration by inflammatory cells. Tumor necrosis factor alpha (TNFα) is a pro-inflammatory cytokine involved in progression of the disease. Under rheumatoid conditions, FLS express the tumor necrosis factor (TNF)-recognition complex (TNFR1, TNFR2, VCAM-1 and ICAM-1), which induces local macrophage activation and leads to downstream nuclear factor κB (NF-κB) signaling. The NF-κB-regulated inflammatory gene, cyclooxygenase (COX), increases synthesis of prostaglandins that contribute to the propagation of inflammatory damage within the joint. Because the nuclear orphan receptor, NR4A2 (Nurr1), can negatively regulate NF-κB-dependent inflammatory gene expression in macrophages, we postulated that activation of this receptor by the Nurr1 ligand 1,1-bis(3'-indolyl)-1-(p-chlorophenyl) methane (C-DIM12) would modulate inflammatory gene expression in synovial fibroblasts by inhibiting NF-κB. Treatment with C-DIM12 suppressed TNFα-induced expression of adhesion molecules and NF-κB regulated genes in primary synovial fibroblasts including vascular adhesion molecule 1 (VCAM-1), PGE2 and COX-2. Immunofluorescence studies indicated that C-DIM12 did not prevent translocation of p65 and stabilized nuclear localization of Nurr1 in synovial fibroblasts. Knockdown of Nurr1 expression by RNA interference prevented the inhibitory effects of C-DIM12 on inflammatory gene expression, indicating that the anti-inflammatory effects of this compound are Nurr1-dependent. Collectively, these data suggest that this receptor may be a viable therapeutic target in RA.